Decreasing effluent loads through bleaching modification

1998

Define pulping and bleaching technology that will decrease or eliminate the release of byproduct organic chlorine compounds without sacrificing bleached pulp quality. PROJECT BACKGROUND' Previous work has included research on the relationship between pulping conditions and bleachability,. improvements to elemental chlorine free (ECF) bleaching sequences, chlorine compound free delignification and bleaching and characterization of bleach filtrates with regard to potential for environmental effect. Previous work on relating softwood pulping conditions to bleachability investigated the effects of effective alkali (EA) charge, sulfidity and anthraquinone. In the Do(EO)D_ sequence, increasing EA increases brighmess ceiling and decreases the amount of C102 needed for a given brightness, while decreasing the kappa number has a similar effect. Effects of EA after full bleaching are more subtle. At normal unbleached kappa numbers, increasing EA increases the brightness ceiling. Addition of anthraquinone (AQ) had a barely noticeable negative effect on the brightness ceiling, but soda and soda-AQ pulps had significantly (2-3 points) lower brightness ceiling than the corresponding kraft and kraft-AQ pulps. Earlier research directed toward improved C102-based ("elemental chlorine free," ECF) bleaching sequences has been centered on two objectives' (1) defining the benefits of a very short retention time chlorine dioxide delignification ("Do") stages and (2) analyzing ECF bleaching process behavior as a route to higher bleaching efficiency and better environmental performance. This work has demonstrated the potential of short retention time Do stages to reduce capital investment and formation of chlorinated organic byproducts. The objectives of earlier research done on nonchlorine delignification and bleaching were (1) to determine the kinetics of delignification and carbohydrate attack by ozone, as a route toward ozone bleaching systems having improved selectivity and (2) to investigate delignification by combinations of oxygen and hydrogen peroxide in the presence of potemially beneficial additives (cyanamide, DTMPA and MgSO4). Research on environmental effects of bleaching filtrates was done in the form of Ph.D. thesis research on the toxicity of filtrates from chlorine and chlorine dioxide delignification sequences after oxygen delignification. A general conclusion was that, by most assays, the chlorine dioxide filtrates were not significantly toxic. The toxicity revealed by more sensitive assays appeared to not to originate in the bleaching stages and was attenuated at higher oxidant charges. The resources available to this project have been effectively leveraged through external funding by the U.S. Department of Energy and, to a lesser extent, the Georgia Consortium for Technological Competitiveness in Pulp and Paper. Project FO13 has contributed a limited amount of matching funds to each of four projects, each of which has goals that are closely aligned with those of Project FO13. During the period March, 1997-February, 1998, our research efforts have included the following: * Peroxide bleaching of softwood kraft pulps produced under systematically varied kraft pulping conditions. , Comparative analysis of (DC)(EO)D_ and Do(EO)D_ bleaching sequences, with respect to effects of kappa factor (KF), effluent carryover and pH in the D_ stage.-Initiation of a study of the effects of oxygen delignification and ECF bleaching on pulp physical properties. , Mill-scale evaluation of"Rapid Do" bleaching (with Project 4201). , Rapid Do bleaching of simulated "Lo-Solids ®'' and conventional kraft pulps at normal and low kappa numbers (with Project 4159). , Gas phase bleaching of conventional and simulated RDH pulps from hardwoods and softwoods (with Project 4159). , ECF bleaching of softwood pulps from controlled liquor concentration profile kraft cooks (with Project 4120).

Chemosphere, 1992

Waste water and its treatment have been studied for pulp and paper manufacturing from sugar cane bagasse and compared to wood pulping and straw pulping. The study included the ability of an activated sludge/aerated lagoon plant to remove chlorophenolics from the effluent, on the basis of a chemical wastewater. This paper is a compilation of the results. The Panchito G6mez Toro Plant is a greenfield integrated pulp and paper mill from 1984 using a modified kraft process based on wet depithed bagasse. The daily pulping capacity is 200 tonnes of air dry pulp (t90). The bleach plant has four stages (C/D E H D). The wastewater treatment is based on aerated, activated sludge and subsequent treatment in a stabilization lagoon with 11 days' retention time. The operation of the activated sludge plant is troublesome due to shock loads of TSS (total suspended solids) and COD (chemical oxygen demand) from the mill, and an inadequate supply of chemicals for coagulation in primary treatment. Consequently, the influent to and the effluent from the activated sludge plant are often high in TSS and COD. The effluent from the lagoon is colored and high in TSS. The quantities of chlorophenolics formed during the bleaching of brown pulp are unexpectedly high. By analogy to a previous study of straw pulp bleaching this is presumably due to high temperatures in the chlorination tower and inappropriate control of chlorine dosing. Generally, chlorophenolics are removed biologically, especially during lagoon treatment. Still, some highly chlorinated and highly substituted phenolics resist the biological wastewater treatment. Conclusions are that aerated stabilization basins are more energy-effective for effluent treatment in tropical zones than activated sludge treatment, and in developing countries they may perform better owing to a better resistance towards shock loads of TSS from improper fiber control in the mill.

Natural Resources, 2011

Journal of Membrane Science, 1995

Today the bleaching stages of the pulp industry are faced with an enormous challenge concerning the minimisation of the environmental impact of its effluents. Organochtorinated compounds (TOX) and mainly the low-molecular-weight fraction of the extractable compounds (EOX) are major pollutants because of their lipophilicity and bioaccumulation ability. This work evaluates the performance of ultrafiltration (UF) and nanofiltration (NF) on the reduction of organochlorinated matter and colour in the effluents from the first alkaline extraction (El) of two different bleaching sequences, one with chlorine/chlorine dioxide and the other only with chlorine dioxide. Three types of membranes were used. Ultrafiltration membranes, CA-400 and ETNA01A, and nanofiltration membranes, CDNF50. The substitution of chlorine/chlorine dioxide by chlorine dioxide in the first bleaching stage reduces 84% of EOX, 82% of TOX and 72% of colour in the E1 effluent. The highest removal of TOX and colour achieved by ultrafiltration is 72 and 92%, respectively. The total removal of colour and more than 90% removal of TOX is achieved by nanofiltration. The two operations, by themselves or integrated, can serve the regulatory and/or mill demands.

Chemosphere, 1999

The degradation, by several advanced oxidation reactions, of a pulp mill ECF bleaching effluent, was studied. The initial biodegradability of the organic matter present in the effluent, estimated as the BODs/COD, was low (0.3). When the effluent was submitted to ozonation and to five different advanced oxidation systems (O3/UV, O3/UV/ZnO, OaAJV/TiO2, O~/UV/ZnO, O2AJV/TiO2), the biodegradability increase significantly. After five minutes of reaction, the O3/UV system appears as the most efficient in to transform the organic matter to more biodegradable forms. A similar effect was observed when the effluent was submitted to an activated sludge treatment. The COD, TOC and toxicity reduction correlated well with the biodegradability enhancement after AOPs treatments.

1999

Environmental concern and tighter public regulations have created new pressures to reduce effluent loading from kraft pulp bleaching during the past decades. This trend has forced both pulp mills and the related engineering industries to develop and optimise equipment for the pulping processes which fulfils these demands. New pulp washers and washing systems connected with the introduction of new oxygen-based reagents have in particular provided considerably improved tools for reusing process water and thereby essentially reducing effluent discharge or even allowing the implementation of a totally closed water circulation system in kraft pulp bleaching. This study was performed mainly on a laboratory scale at the University of Oulu, but some pilot-scale tests were also performed to confirm the findings of the laboratory-scale evaporation test. Another aim of the pilot-scale tests was to produce enough concentrate for further processing. Conditions were strictly controlled in all the experiments in order to ensure that conclusions could be reached regarding the phenomena examined. The results reported here indicate that the amounts of transition metal ions such as iron, copper or manganese in the process water or water to be recirculated should be kept as low as possible during chlorine dioxide or peracetic acid bleaching, as even a small amount (<<5 ppm) markedly reduced pulp quality and increased reagent consumption. The results also show that evaporation can be used as a method for purifying acidic effluent from both chlorine dioxide and peracetic acid bleaching, and that the resulting condensates were free of transition metals and clean enough for reuse in both bleaching processes. The purity of the condensates was further improved by neutralising the feed pH of the acidic effluents from the bleach plant before evaporation. The results also indicate that the chloride ions in the concentrate arising from evaporation of the acidic effluent from chlorine dioxide bleaching can be removed by a combined acidification/re-evaporation system.

Revista Árvore, 2016

The main objective of this work was to study the technical viability of using the cellulose bleaching effluent, at several stages of the process, seeking fresh water reduction in pulp washing, and evaluating its effect on pulp quality. Eucalyptus spp. industrial cellulosic pulp with oxygen was used in this experiment. The same bleaching sequence D(E+P)DP was performed ten times, under the same conditions (temperature, consistency and time). Counter current washing was used in the bleaching stages, and each sequence was carried out with different washing factors: 9, 6, 3, 0 m3 of distilled water/ton of pulp, trying to reach brightness of 92 ± 0,5% ISO. The ten sequences sought to achieve the stability of the effluent organic load, measured by the chemical oxygen demand (COD). Then, the COD results were compared to the brightness ones from the bleached pulp. The evaluated results from the ten sequences and four different washings showed an increasing in COD due to the organic load acc...

We investigated the bleaching efficiency of the final chlorine dioxide (D2) stage in the D0(EP)D1D2 bleaching sequence, focusing on the effect of pH in relation to the bleaching history of pulp samples. The samples used were unbleached kraft Eucalyptus grandis pulps with kappa no. 14.8 and the same pulp oxygen-delignified to kappa nos. 12 and 9.8. The samples were bleached according to the D0(EP)D1 sequence to a brightness of about 86% ISO and then submitted to the final D2 stage under identical conditions (e.g., chlorine dioxide charge, time, tempera¬ture, and final pH). The target final brightness was 90.5% ISO. Changes in the kappa number, brightness, viscosity, and contents of hexenuronic acid), 4-O-methylglucuronic acid, and the total amount of carboxylic acid (COOH) groups in pulps were monitored during the bleaching sequence. The final brightness of eucalyptus kraft pulps increased when the terminal pH of the D2 stage was raised from 3.0 to 6.5. The 90.5% ISO target brightness in the D2 stage was achieved for all pulps within a pH range of 4.5–6.5, but this required adjusting final pH for individual sam¬ples. The optimal pH value with respect to pulp viscosity was between 3 and 5. Despite dissimilar conditions applied in previous bleaching stages, the samples after the D1 stage revealed similar residual lignin contents as shown by kappa number analysis. The content of hexenuronic acid in the samples, however, varied broadly, from 2 to 26 mmol/kg. Conductometric titration showed different amounts of carboxylic acid groups in pulps after the D1 stage, of which hexenuronic acid accounted for only a minor part. The variations in the fiber charge resulted from the different bleaching conditions applied before the D2 stage. The fiber charge affected the alkali demand in the final D2 stage, whereas variations in the alkali demand affected the initial pH and associated process kinetics. Lower total fiber charge was found to be beneficial for improved final brightening and viscosity when bleached at higher final pH.

October 2013, 2013

This work evaluates the findings of various research efforts and describes the development, use, and benefits of applying techno-economic models of different types to various production and bleach plant scenarios. During the late 1980s and early 1990s, researchers determined that bleach plants were releasing potentially significant quantities of chlorinated organics into receiving waters. This led to extensive research to develop bleaching chemicals to eliminate chlorine and hypochlorite from the bleaching sequence. Over time, 100% chlorine dioxide substitution for chlorine became the industry standard (today’s elemental chlorine free [ECF] bleaching), and research efforts shifted toward chemical optimization of the ECF bleaching sequence. Several delignification stage and brightening stage models were developed and refined for use in bleach plant simulations to optimize chemical performance. Advances in computing power and the availability of packaged spreadsheet and simulation pro...

Adsorbable organic halogen (AOX) is mainly produced by the reaction of residual lignin and chlo-rinated bleaching agents during bleaching processes. The formation of AOX can be reduced via optimization, addition of chemical additives, and/or pretreatment processes. Only a few studies exist on the effective purification of chlorine dioxide solutions and its effect on AOX reduction. In this paper, the effects of the extraction pressure, temperature, pH, and extraction time on the chlorine gas removal rate (CR) were evaluated. In addition, a response surface model was established to optimize the chlorine gas removal. The temperature of chlorine gas separation was optimized at 39.85 * C, with a separation pressure of 51.20 kPa and solution pH of 1.94, providing an estimated CR of 70.93% under the optimum separation conditions. Chlorine dioxide solutions with and without chlorine gas removal were used for pulp bleaching. AOX formation was reduced by 69.57% at the same 2.0% chlorine dioxide dosage, while the pulp brightness decreased by 3.0%ISO. In addition, AOX formation was reduced by 27.90% at the same bleached pulp brightness (80.00%ISO). The results provide theoretical support for the production of high-purity chlorine dioxide solutions and the development of clean pulping and papermaking processes.